Conventionally, drip irrigation systems (also known as trickle irrigation systems or micro irrigation systems) have been employed to supply water and irrigation liquid such as liquid fertilizer to the plants to be grown into the soil in the agricultural land, the plantation or the like.
In such drip irrigation systems, for example, a filter, a fertigation apparatus (a chemigation apparatus if necessary), a back flow prevention apparatus, a main pipe, and the like are connected in sequence on the downstream side of a pump that brings up water from the water source, and an elongated drip watering tube is connected to the channel terminal. In addition, the drip watering tube is laid on the soil in which plants are grown.
Here, the drip watering tube ejects the irrigation liquid in the tube main body at a predetermined ejection rate (or ejection speed) per unit time from a plurality of ejection ports provided to the elongated tube main body at predetermined intervals along the longitudinal direction of the tube main body. Thus, the irrigation liquid is slowly supplied to the soil outside of the drip watering tube (that is, drip irrigation is performed).
With such a drip watering tube, water and fertilizer can be saved. In addition, by supplying water at a moderate supply speed, the oxygen required for plant roots can be ensured in the soil. As a result, the growing of plants can be favorably managed.
In such a drip watering tube, a drip irrigation emitter for controlling the ejection amount of the irrigation liquid from each ejection port per unit time is provided at each ejection port.
In this drip irrigation emitter, the irrigation liquid flowing in the tube main body flows in the drip irrigation emitter through the inlet and flows through a pressure reduction channel (which is called labyrinth) in the drip irrigation emitter in such a manner that the pressure of the irrigation liquid is reduced, and then, the irrigation liquid is ejected from the ejection port connected on the downstream side of the pressure reduction channel.
Some conventional drip irrigation emitters are provided with a so-called differential pressure control mechanism (pressure correction function). Such conventional drip irrigation emitters have, for example, a three-component structure in which an elastic film (for example, silicone rubber film) such as a diaphragm is sandwiched by an inflow side member and an ejection side member, as with the drip irrigation emitter (emitter unit) disclosed in PTL 1.
The drip irrigation emitter disclosed in PTL 1 controls the opening/closing of the entrance port of the drip irrigation emitter and the flow rate from the exit port of the drip irrigation emitter, by the operation of a diaphragm (film) in accordance with the liquid pressure outside of the drip irrigation emitter and in a tube main body.
To be more specific, in the drip irrigation emitter disclosed in PTL 1, when the liquid pressure outside of the drip irrigation emitter is increased to a certain level, the diaphragm that is so disposed as to shield the entrance is deflected by the liquid pressure toward the outlet. As a result, the entrance is opened. When the liquid pressure is further increased, the amount of the deflection of the diaphragm toward the outlet is increased, and consequently the cross-sectional size of the channel in the outlet is reduced. As a result, the ejection amount is limited.
As disclosed in paragraph [0004] of PTL 1, in the drip irrigation emitter, the ejection speed of the irrigation liquid from the drip irrigation emitter (emitter) has substantially no relation with the variation in pressure of the irrigation liquid supplied to the drip irrigation emitter.
Therefore, the drip irrigation emitter has been expected to limit non-uniformity in the ejection amount of the irrigation liquid between the drip irrigation emitters disposed on the upstream side (high pressure side) and the downstream side (low pressure side) in the tube main body, to thereby uniformize the growing of plants in the entire soil.